1. Field of the Invention
The present invention pertains to the field of computer graphics devices. More particularly, this invention pertains to the field of improving processor to graphics device local memory performance.
2. Background of the Related Art
Computer systems perform a variety of functions including data acquisition, data processing, and display of graphical or video images. The images displayed to the user can take many forms. For example, it may be useful to display information in terms of alphanumeric characters, graphical images, or even full motion video. In any of these forms, the user seeks to maximize the quantity and quality of information that is output to the display, as well as maximizing the speed at which the information is displayed. Many of today's applications, including 3D games, video conferencing, and movie playback, place large strains on computing and display resources. These computing and display resources may include a microprocessor, a system memory, a graphics device, a local memory for the graphics device, and a system bus for interconnecting the processor, system memory, and graphics device. Images are output from the graphics device to a display monitor for display.
As mentioned above, a local memory is generally implemented in conjunction with a graphics device in a computer system. The local memory may be referred to as a frame buffer. The local memory contains pixels in a digitized form for display on the corresponding display monitor. The pixel data is arranged in the frame in rows and columns that correspond to rows and columns on the display monitor. To display a graphical image on a display monitor, the pixel data is transferred from the local memory and converted to an analog signal by a digital to analog converter (DAC) within the graphics device.
In order to process and prepare images for display, the processor, as well as the graphics device, must access the local memory. The speed at which the processor is able to retrieve information from or store information to the local memory directly effects the quality of displayed images as well as the speed at which the images are displayed. In a typical implementation, the processor's path to the frame buffer is through the graphics device. The processor is typically able to communicate with the graphics device with relatively little latency and with reasonable bandwidth. However, when the processor must access the frame buffer, the latency increases greatly and the bandwidth is severely reduced. This increase in latency and reduction in bandwidth is due to the large latency that is introduced by the path through the graphics device. One reason for the large latency that is introduced by the path through the graphics device is that the processor must compete for access to the frame buffer with several functional units within the graphics device, including, but not limited to, rendering engines, blitter engines, and display engines. In general, and as well known in the art, rendering engines process images, blitter engines move image data from unit to unit and between system memory and local memory, and display engines output the processed and prepared images for display on a display monitor.
Previous graphics devices have assigned a low priority to processor accesses to the local memory. The several units in the graphics device are assigned priorities equal to or greater than the processor for accesses to the local memory. This results in poor processor to local memory performance, and this in turn adversely effects graphics performance. Therefore, a method and apparatus for improving processor to graphics device local memory performance is desirable.